The present invention relates generally to an electrophotography, and more particularly to an electrophotographic apparatus which comprises a document feed mechanism for advancing a sheet like document and a thick document such as a book placed on a thick document carriage through a light exposing portion.
Various kinds of electrophotographic apparatuses have heretofore been proposed and used in practice. One of these conventional electrophotographic apparatuses is mainly used for obtaining copies of a thick manuscript or document such as books or the like, while the other electrophotographic apparatus is mainly used for obtaining copies of a sheet manuscript.
In the electrophotographic apparatus mainly used for obtaining copies of the thick manuscript, in the case of obtaining copies of the sheet manuscript, the sheet manuscript is disposed on a manuscript carriage and urged against it by a manuscript holding cover. The manuscript carriage or a projection optical system is reciprocated for number of times corresponding to the number of sheets to be copied, thereby obtaining copies. In this case, the operation of opening and closing the manuscript holding cover in order to set the sheet manuscript on the manuscript carriage is troublesome in operation. In addition, wind pressure produced when the manuscript holding cover is opened and closed tends to displace or blow off the sheet manuscript set beforehand, thereby rendering the operation very inconvenient and bad in efficiency. In general, the kind of the manuscript to be copied belonging to the sheet manuscript is far larger than that belonging to the thick manuscript. As a result, the above is the important drawback inherent to the electrophotographic apparatus mainly obtaining copies of the thick manuscript.
On the other hand, the electrophotographic apparatus mainly used for obtaining copies of the sheet manuscript is classified into one type in which the sheet manuscript is directly inserted into and passes through a light exposure portion so as to be scanned by exposed light and into another type in which if the sheet manuscript is introduced into the apparatus it is automatically set to a given position where it is repeatedly scanned by the exposed light for the number of times corresponding to the number of the copies to be obtained and then is automatically discharged from the apparatus.
The former type electrophotographic apparatus can insert the sheet manuscripts in succession into the light exposure portion and hence is very rapid in operation if compared with the above mentioned electrophotographic apparatus mainly used for obtaining copies of the thick manuscript and adapted to change a previous manuscript to the next manuscript after the previous manuscript has been scanned by the exposed light.
In addition, the former type electrophotographic apparatus is not required to use a reciprocating mechanism for the manuscript carriage or projection optical system, so that the apparatus as a whole is simple in construction and can be manufactured in a less expensive manner. But, in the case of obtaining a plurality of copies from the same manuscript, the manuscript must repeatedly be inserted into the light exposure portion for number of times corresponding to the number of copies to be obtained, and as a result, the apparatus becomes very troublesome in operation and bad in efficiency.
The latter type electrophotographic apparatus has the advantage that a desired number of copies can be obtained by inserting the sheet manuscript only one time into the apparatus. But, this apparatus has the drawback that the apparatus as a whole is complex in construction, that a manuscript feed path in complex in construction and hence is troublesome in feed operation and that the manuscript tends to be easily broken.
The former type electrophotographic apparatus can obtain copies of the thick manuscript with the aid of a suitable auxiliary means. On the contrary, it is almost impossible to obtain copies of the thick manuscript by the latter type electrophotographic apparatus. To the electrophotographic apparatus mainly used for obtaining copies of the thick manuscript has been added a sheet manuscript feed mechanism which can automatically feed a sheet manuscript disposed on a manuscript carriage and automatically discharge it after a required number of sheets have been repeatedly scanned by the exposed light. But such kind of sheet manuscript feed mechanism is complex in construction and large in size and hence is generally used for an expensive high speed copying machine.
The auxiliary means added to the former type electrophotographic apparatus mainly used for obtaining the sheet manuscript and operative to obtain copies of the thick manuscript comprises a sheet manuscript driving roller, its corresponding driven roller and an end driven roller independent of the driven roller and arranged at the outside of the driven roller, the end driven roller being co-operative with the driving roller so as to feed a light transmission thin plate for the thick manuscript and constructed such that in the case of obtaining copies of the thick manuscript the sheet manuscript feed driven roller is pushed aside or removed and the light transmission thin plate with the thick manuscript disposed thereon is held between the driving roller and the end driven roller so as to be fed and scanned by the exposed light. That is, the light transmission thin plate formed such auxiliary means is fed at a given feed speed by means of a fractional force produced between the plate and the driving and end driven rollers. But, in the case of obtaining copies of the thick manuscript by means of such auxiliary means, an operator is always required to hold down the thick manuscript by a pressure which is sufficient to prevent the thick manuscript from displacing or from rising during feed of the transparent thin plate. As a result, unreasonable force is subjected to the thin plate while it is fed. The frictional force produced between the driving roller and the end driven roller for feeding the light transmission thin plate sandwiched therebetween becomes changed. As a result, it is impossible to maintain the given feed speed, thereby inducing a blur in copy or an inclined displacement of the transparent thin plate. Further, it is necessary to feed the thick manuscript carriage in such a manner that the transparent thin plate can be correctly positioned between the rollers. As a result, in the case of using such auxiliary means, the operator is required to have a certain order of skill and operate with the greatest possible care. In addition, the end driven roller is projected from the surface along which the thin plate passes, so that the operator is also required to pay attention not to damage his finger or the manuscript got caught in the projected end driven roller.
In the case of obtaining a plurality of copies from the same manuscript, the above mentioned operation must be repeated, so that the operation becomes more complex and the rate of damaging the precious manuscript becomes high. In addition, the separate need of the driven roller exclusively used for feeding the thick manuscript makes the apparatus complex in construction.